1. Field of the Invention
The invention relates to ball screw technology, and more particularly, to a tunnel raceway type ball screw assembly, which greatly enhances durability and cycling stability.
2. Description of the Related Art
Many ball screw designs are known. Japanese Patent 2010-090953 discloses the establishment of a cycling channel on the surface of a screw shaft for enabling balls to cycle along an outer thread groove of the screw shaft. However, this cycling channel simply extends over one single thread lead. For an application that the lead is kept in proximity to the ball diameter, ball impact can be a concern if the tooth thickness between one groove to another is excessively thin. Further, Taiwan Patent M472136 adopts a similar cycling channel design that extends across one single lead. However, this design has the same problem as the aforesaid prior art Japanese patent. Further, if a design to shift a pitch is adopted, it will encounter a spatial arrangement problem. Further, Japanese Patent 2005-201347 discloses a stepped design to guide the balls, however, this design has the drawbacks of processing difficulties and poor cycling stability.